Lithium secondary batteries have the advantages of high energy density, little self-discharge, excellent long-term reliability and the like, and are therefore broadly put to practical use as batteries for small-size electronic devices such as laptops and cellular phones. In recent years, high functionalization of electronic devices and utilization of lithium secondary batteries for electric cars have progressed, and the development of higher-performance lithium secondary batteries is thus demanded.
At present, carbon materials are common as negative electrode active materials for lithium secondary batteries, and various types of carbon materials are proposed in order to improve the battery performance.
For example, Patent Literature 1 discloses an electrochemical power storage device using as an electrode active material a C/Si/O composite material obtained by impregnating a graphite having voids with an organosilicon compound selected from silanes and siloxanes, forming a crosslinked substance of the organosilicon compound, and heating the resultant (in a non-oxidizing gas, 600° C. to 1,400° C.) to react the crosslinked substance with the graphite. Patent Literature 1 further discloses that the use of the electrode active material particularly for a negative electrode of a lithium ion secondary battery can provide an electrochemical device having a high capacity and being excellent in cycle characteristics.
Patent Literature 2 discloses a negative electrode active material for a lithium secondary battery which contains a graphite core which can intercalate and deintercalate lithium and has pores running from its external surface to its interior, metal nanoparticles dispersively disposed in the pore interiors, and an amorphous carbon filled in the pore interiors. Patent Literature 2 also discloses that the use of the negative electrode active material for the lithium secondary battery improves the capacity maintenance rate and the charge and discharge efficiency.
Patent Literature 3 discloses a carbon material which has voids in its interior and contains metal-including hollow carbon particles containing a metal (silicon or the like) to form an alloy with lithium. Patent Literature 3 discloses that the carbon particle is formed by gathering up a large number of fine grains (matrixes composed of carbon) with a plurality of bores mutually connected in gaps between the grains, and that the carbon particle can further contain a conductive auxiliary agent such as graphite. Patent Literature 3 also discloses that such a carbon material is suitable as a negative electrode material for a lithium ion secondary battery, has a high lithium-intercalating and deintercalating capacity, and hardly damages even if being subjected to successive charges and discharges.